Effect of calcination temperature on the microstructure, crystallinity and photocatalytic activity of TiO2 hollow spheres

Submicrometer-sized TiO2 hollow spheres (THS) were synthesized using a template method, which involves deposition of TiO2 on SiO2 spheres templates through sol–gel process, calcination to crystallize amorphous TiO2, and etching SiO2 templates by hydrothermal treatment in NaOH solution. The evolution of the microstructure, crystallinity and photocatalytic activity of the THS fabricated with TiO2@SiO2 calcined at various temperature were studied systematically. The calcination treatment allows crystallization of the amorphous TiO2 shell into anatase nanocrystals in temperature range of 400–800 °C, and the crystallinity of the anatase TiO2 nanocrystals is improved as the calcination temperature increases. At temperature above 1000 °C, partial anatase TiO2 transforms to rutile phases. The morphology and microstructure of THS also varied over the calcination temperature due to the growth and aggregation of TiO2 nanocrystals. Accordingly, the absorption spectra edges of the THS shift towards the long wavelength. The results of photodegradation of Rhodamine B (RhB) under ultraviolet (UV) light illumination indicated that the THS calcined at 800 °C exhibited the highest photocatalytic activity, benefiting from the high crystallinity of anatase TiO2 and hierarchical hollow spherical structure.

► TiO2 hollow spheres (THS) were synthesis using a template method.
► Calcinations were carried out to crystallize TiO2.
► Calcinations temperature affects the microstructure and crystallinity of THS.
► THS-800 exhibits high anatase crystallinity and hierarchical hollow structure.
► THS-800 shows superior photocatalytic activity under UV light illumination.